The longer you have been around, the more the landscape shifts.
We often learn just enough to move forward.
You might even study intently.
But then, you may have studied and learned a feature set that has since had more features published/released.
Looking at some tan-stack table code today ran into some typescript that was foreign to myself: link.
According to the typescript docs this is called optional-element-access, which lets you access both objects and arrays with strings and/or numbers.